Front Derailleur Adjustment (Taking SHIMANO DEORE LX as an example):Follow the following simple rules for repeated adjustments H screw — Used to adjust the positioning of the chain at the largest chainring. Counterclockwise (unscrewed out): the front derailleur arm moves away from the seat tube; clockwise (screwed in): the front derailleur arm moves closer to the seat tube. Note: Be careful with the degree when turning counterclockwise (unscrewed out), as going too far may cause the chain to come off the chainring and get stuck between the crank and the large chainring, which is very dangerous. L screw — Used to adjust the positioning of the chain at the smallest chainring. Counterclockwise (unscrewed out): the front derailleur arm moves closer to the seat tube; clockwise (screwed in): the front derailleur arm moves away from the seat tube. Note: Be careful with the degree when turning counterclockwise (unscrewed out), as going too far may cause the chain to come off the chainring and get stuck between the bottom bracket and the small chainring, which is very dangerous.
Rear Derailleur Adjustment (Taking SHIMANO DEORE LX as an example):Follow the following simple rules for repeated adjustments:
Screw 1— Used to adjust the positioning of the chain at the smallest cog. Counterclockwise (unscrewed out): the rear derailleur arm moves away from the wheelset; clockwise (screwed in): the rear derailleur arm moves closer to the wheelset. Note: Be careful with the degree when turning counterclockwise (unscrewed out) or clockwise (screwed in), to ensure that the smallest cog and the rear derailleur guide pulley are in the same plane.
Screw 2— Used to adjust the positioning of the chain at the largest cog. Counterclockwise (unscrewed out): the rear derailleur arm moves closer to the wheelset; clockwise (screwed in): the rear derailleur arm moves away from the wheelset. Note: When turning counterclockwise (unscrewed out), be careful with the degree, as going too far may cause the chain to come off the cog and get stuck between the spokes and the cassette, which is very dangerous.
Screw 3— Fine-tuning. Counterclockwise (unscrewed out): the rear derailleur arm moves closer to the wheelset; clockwise (screwed in): the rear derailleur arm moves away from the wheelset.
In addition, the split-type shifters also have a fine-tuning screw identical to Screw 3, which can be used to fine-tune the front and rear derailleurs.
For Screw 1, we can see an “H” marking nearby, which stands for high, i.e., the high gear limit screw we often talk about. The function of this screw is to adjust the distance the rear derailleur retracts toward the smaller sprockets. If this screw is too tight, when the gear display shows 7, 8, or 9 on a 7-speed, 8-speed, or 9-speed system, the chain cannot reach its position and will jump between the smallest cog and the second-smallest cog. If you turn this screw counterclockwise to make it too loose, the chain may jump beyond the smallest cog (chain drop). Therefore, this screw specifically controls the final position of the chain around the smallest cog.
Screw 2 has an “L” marking, which stands for low, i.e., the low gear limit screw we refer to. This screw controls the position of the chain on the largest cog. When adjusted properly, the chain can smoothly enter the large cog without derailing inward into the space between the cog and the spokes, nor will the rear derailleur directly contact the spokes. If this screw is too loose, it may cause either of these two issues, while if it’s too tight, it may prevent the chain from shifting onto the largest cog or cause the derailleur to jump between the largest and second-largest cogs when the shifter is in the first gear.
Screw 3 is what we commonly call the cable tension adjustment screw. Tension is adjusted by turning this part counterclockwise or clockwise, and the result is to ensure that when the shifter controlling the rear derailleur is actuated, the chain accurately stays in the corresponding gear. The adjustment direction is: turning counterclockwise increases cable tension, while turning clockwise reduces it. This is the function of the unmarked fourth screw, and this screw is also the cause of noise on smaller cogs. If this screw is not tightened, it may cause the chain to wrap around the small cog, creating noise.
There is also a rear derailleur retraction tension screw not mentioned here, which is the one located above the H screw and pressing against the hook. This screw also has a certain impact on shifting. In Shimano systems, it’s not very noticeable—just a bit looser increases friction and wear, while tightening makes it easier to jump cogs. But in SRAM’s single-spring systems, if this screw isn’t adjusted properly, it can lead to inaccurate positioning of the entire system, especially when shifting to the large chainring. I had a long discussion with Yiyiguxing about this before, and only later realized that the problem was with that screw.
Q: When I use the smallest chainring on my front derailleur, there is slight friction between the chain and the front derailleur. How should I adjust it? Should I adjust the H screw?
A: I’m not sure where the chain is positioned on the rear cog when you’re using the smallest chainring. If the chain is on the smallest cog (though such a combination is rare), some slight friction between the chain and the front derailleur is inevitable. If the chain is on the largest cog and there’s slight friction with the front derailleur, you can turn the L screw counterclockwise (make a slight adjustment). Of course, whether the front derailleur shifts accurately also directly relates to its initial installation position on the seat tube. Since I’m not entirely clear about your specific situation, I’m just explaining based on principle. It mainly depends on your own experience and practice.
Q: I also want to ask, yesterday while riding, I found that when shifting from the 1st (smallest) chainring to the 2nd chainring, the chain wouldn’t shift up. But shifting from the 1st chainring to the 3rd (largest) chainring, the chain could shift up accurately. Then shifting from the 3rd chainring to the 2nd chainring, the chain could shift up accurately. How should I adjust this?
A: Based on your description, it seems the chain can’t shift from the small chainring to the middle chainring, but other shifts are fine.
How about this: With the chain on the small chainring, turn the L screw clockwise (slightly) or the fine-tuning screw on the split-type shifter counterclockwise (step-by-step fine-tuning). You’ll notice that the front derailleur arm gradually moves away from the seat tube (the front derailleur arm moves outward). Adjust while testing until the chain can shift smoothly. At the same time, make sure the shifting on other gears remains smooth. If adjusting affects the smoothness of other gears, I suspect it might be due to initial errors in the tension of the front derailleur cable or the installation position of the front derailleur on the bottom bracket.
Q: I also want to ask, yesterday while riding, I found that when shifting from the 1st (smallest) chainring to the 2nd chainring, the chain wouldn’t shift up. But shifting from the 1st chainring to the 3rd (largest) chainring, the chain could shift up accurately. Then shifting from the 3rd chainring to the 2nd chainring, the chain could shift up accurately. How should I adjust this?
A: Hello, this is because the cable is slightly too loose. You only need to make a slight counterclockwise adjustment at the red circle on the right side of Figure 3. But if you’re riding a mountain bike, it’s actually best if shifting from 1 to 2 is a bit harder, while shifting from 3 to 2 is easy. This is because under climbing pressure, the chain often doesn’t shift down easily, and shifting from 1 to 2 with slightly more pressure on the lever is also relatively easy. If you adjust it so that shifting between 3rd gear is smooth on flat ground, it might actually be harder to shift down when climbing, and not being able to shift down while climbing can force you to dismount. So, the key to front derailleur adjustment is ensuring it can shift down smoothly.
I also mentioned in previous posts that the initial installation position of the front derailleur on the seat tube is crucial, directly affecting the derailleur’s performance across different chainrings (smooth and accurate gear shifts).
1. Initial Installation of the Front Derailleur:Install the front derailleur on the seat tube, slightly tighten the band clamp fixing screw so that it has some friction with the seat tube but can still move up and down and rotate left and right relatively freely.
2. Spacing Positioning:Use the pre-set alignment block that comes with the front derailleur (you can also use something like a toothbrush handle as a substitute) to lift the front derailleur guide plate so that the outer guide plate surface is in the same plane as the large chainring. Move the front derailleur up and down along the seat tube to keep the distance between the outer guide plate and the chainring teeth within the range of 1–3 mm. At this point, slightly tighten the front derailleur band clamp fixing screw, which means the vertical position of the front derailleur on the seat tube has been determined.
3. Horizontal Positioning:Control the force and rotate the front derailleur left and right on the seat tube (be careful not to move it up or down), adjusting it more precisely so that the outer face of the front derailleur guide plate aligns with the face of the large chainring — that is, determine the left-right position of the front derailleur on the seat tube. At this point, fully tighten the front derailleur clamp fixing screw. With this step, the front derailleur without cable tension is now positioned correctly on the seat tube.
4. Cable Fixing:Thread the cable through at the position indicated by the cable fixing screw. Place the hex wrench on the screw in preparation for tightening. Use the cable cutter to grip the cable end and pull with steady force — at this time, the pre-set alignment block that pads the front derailleur guide plate may fall off, but that’s okay. Continue to control the force and direction while pulling until the outer face of the front derailleur guide plate aligns with the face of the large chainring, then quickly tighten the cable fixing screw. Here’s a reminder: when performing this step, ensure that the front derailleur’s shift lever is set to position 2 (i.e., aligned with the middle chainring). Any subsequent fine adjustments will refer back to the instructions described earlier.